So my story:
My pc was running kinda good for month or so,I had a couple random restards maybe one blue screen,so I did rune auto tune for some oc testing and had black screen restarted good to go everything was fine so I decided to buy new heatsink becouse I thought it was cooling problem too high temperature, Thermalright 140mm True Spirit Fan with 6x Copper Heat Pipes, so I installed, with a bit too much thermal paste but it was runing just fine so I decided not to go inside agian and started amd catalysts auto-tune on my cpu, wanted to oc a bit with new heatsink, so it was runing for a few minutes (2-4min) and then I lost signal to my monitor it went black and pc was still runing agian, so I did turn off the pc, when I turned back on same thing pc was runing, no beeps no boot no signal to monitor, so I cleard the cmos did not help, so I changed my psu becouse I think is a bit to weak for my build and I cloude have killded, so I got corsair tx750 didint help, so it is MOBO or CPU, but I dont think it is cpu it is hard to kill, I had a look on it looks like new no marks or stuff like that, and auto tune was runing only for a few minutes, I did try reasamble my pc same thing, so what you think? How can I test it CPU or MOBO, no spare parts, it is hard to tell no beeps no boot, no keybord ligths no usb power, so can it be mobo? And cpu fan is spining a bit slow

A couple things stick out in your story there.
1) the Gigabyte 970A-DS3 with a 4+1 VRM/power phase is not ideal for the likes of the FX-8350, much less overclocking it. The Top end 125W FX line should really be paired with a 990FX 8+2 powered board.
2) You acknowledged that you put it together with

a bit too much thermal paste but it was runing just fine so I decided not to go inside agian

Click to expand...

That usually means a whole lot too much, and you should have reapplied the thermal compound correctly before reassembly. when the TIM warms up too much of it can drip/run down the board shorting it out, or end up in the pin holes. I would dtart with a visual inspection to see if the superfluous TIM end up where it's not suppose to be.
3) (and the one my money is on) you may have noticed the rows of naked MOSFETS behind the row of inductors. you have one of the few boards with no VRM heatsink and I happen to know that they were scorching hot under normal circumstances, much less attempting to overclock the FX -8350.
those are some things to consider, however as Richard dryfuss said in 'Jaws', " I think were gonna need a bigger board"...or something like that.